JP2003213203A - Polyester resin for powder coating material, its composition and powder coating material using the composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a polyester resin for a powder coating material not causing yellowing with time and capable of obtaining a matte coated film, its composition and a powder coating material using the resin composition. <P>SOLUTION: The polyester resin for the powder coating material is composed of an acid component consisting mainly of an aromatic dicarboxylic acid and an alcohol component containing ≥80 mol% neopentyl glycol and has 0.10-0.30 dl/g limiting viscosity, 10-30 mgKOH/g acid value and ≥7 mgKOH/g hydroxy value. The polyester resin composition for powder coating material comprises the polyester resin, an epoxy resin curing agent having ≤250 g/eq epoxy equivalent, a curing agent having a functional group reacting with hydroxy group of the polyester resin and a matting agent at a specific ratio. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a polyester for powder coatings, which is capable of obtaining a matte coating film which is excellent in weather resistance without yellowing over time, and which is excellent in smoothness and mechanical strength. The present invention relates to a resin and a composition, and a powder coating material using the same.

[0002]

2. Description of the Related Art Compared with conventional solvent-based paints, powder paints are non-polluting paints, can be used immediately after painting, do not require multi-layer coating, and are relatively inexpensive. It has been recognized that there are advantages such as the fact that it can be recovered and used, and in recent years, the demand has rapidly expanded as a coating material for protection and decoration of members such as building materials, home electric appliances and automobile parts.

Epoxy resin-based, acrylic resin-based, and polyester resin-based powder coatings are mainly known as powder coatings, and polyester resin-based powder coatings are known as coatings having a balanced coating performance. Has been. Among them, the polyester-epoxy hybrid powder coating composed of a polyester resin whose main terminal is a carboxyl group and an epoxy resin-based curing agent is excellent in economic efficiency and corrosion resistance,
Since a good matte coating film can be obtained by adding a matting agent, it is often used for steel shelves and home appliances.

On the other hand, since these polyester-epoxy hybrid matte powder coatings contain a large amount of epoxy resin, there is a problem that the weather resistance of the coating film is not good and it yellows over time. In order to improve the weather resistance of the coating film and suppress yellowing, studies have been conducted to reduce the amount of epoxy resin-based curing agent added, but the mechanical properties of the coating film deteriorate as the crosslink density decreases. However, there is a problem that the matting effect cannot be obtained, and a matte powder coating that does not yellow with time and weather resistance has not yet been developed.

[0005]

The present invention solves the above problems and has a polyester resin and a composition for powder coatings, which is capable of obtaining a matte coating film which is excellent in weather resistance and does not yellow with time. And a powder coating material using the same.

[0006]

The present inventors have arrived at the present invention as a result of repeated research to solve the above problems.
That is, the gist of the present invention is as follows. (1) The acid component is mainly an aromatic dicarboxylic acid, 80 mol% or more of the alcohol component is neopentyl glycol, the intrinsic viscosity is 0.10 to 0.30 dl / g, the acid value is 10 to 30 mgKOH / g, And the hydroxyl value is 7m
Polyester resin for powder coatings, characterized by having gKOH / g or more. (2) The polyester resin described in (1) above, an epoxy resin-based curing agent having an epoxy equivalent of 250 g / eq or less, a curing agent having a functional group that reacts with a hydroxyl group of the polyester resin, and a matting agent are represented by the following formulas and A polyester resin composition for a powder coating material, which is contained at a ratio to satisfy the requirement. 0.8 ≦ (A + B) /C≦1.2 ... 0.3 ≦ A / B ≦ 0.9, where A is the amount (equivalent amount) of carboxyl groups in the polyester resin, B is the amount of carboxyl groups in the matting agent (equivalent), and C is the amount of epoxy groups contained in the epoxy resin-based curing agent (equivalent). (3) A powder coating material using the polyester resin composition for powder coating material according to (2) above.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below. It is necessary that 80 mol% or more of the alcohol component of the polyester resin of the present invention is neopentyl glycol. The copolymerization amount of neopentyl glycol is 8
If it is less than 0 mol%, sufficient weather resistance cannot be obtained. The upper limit of the copolymerization ratio of neopentyl glycol is not particularly limited, and it can be used up to 100 mol%.

Other than the above-mentioned neopentyl glycol, as alcohol components, ethylene glycol, diethylene glycol, 1,2-propylene glycol, 1,3-propanediol, and 1-propanediol may be used, if necessary, as long as the effects of the present invention are not impaired. Aliphatic glycols such as 1,4-butanediol and 1,6-hexanediol, alicyclic glycols such as 1,4-cyclohexanedimethanol and 1,4-cyclohexanediol, ethylene oxide adducts of bisphenol A, and bisphenol S A small amount of an aromatic glycol such as an ethylene oxide adduct or a trihydric or higher alcohol such as trimethylolpropane, glycerin or pentaerythritol may be used in combination.

As the acid component, it is necessary to mainly use an aromatic dicarboxylic acid in order to exhibit various performances when used as a paint or a coating film. As the aromatic dicarboxylic acid, terephthalic acid and isophthalic acid are mainly used. Aromatic dicarboxylic acids and their ester-forming derivatives, succinic acid, adipic acid, azelaic acid, sebacic acid, dodecanedioic acid and other aliphatic dicarboxylic acids, cyclohexanedicarboxylic acid and other alicyclic dicarboxylic acids, trimellitic acid, trimesic acid A small amount of trivalent or higher carboxylic acid such as pyromellitic acid or oxycarboxylic acid such as 4-hydroxybenzoic acid and ε-caprolactone may be used in combination.

The polyester resin of the present invention must have an intrinsic viscosity of 0.10 to 0.30 dl / g,
It is preferably 0.15 to 0.25 dl / g. If the intrinsic viscosity of the polyester resin is less than 0.10 dl / g, the blocking resistance of the resin and the smoothness of the coating film are deteriorated due to the low molecular weight of the resin, which is not preferable. on the other hand,
When it exceeds 0.30 dl / g, the pulverizability is deteriorated due to the high molecular weight of the resin and the fluidity is deteriorated, so that the smoothness of the coating film is deteriorated. Further, the amount of the epoxy resin-based curing agent compounded is small, and a matte coating film cannot be obtained, which is not preferable.

The polyester resin of the present invention has an acid value of 10
It is necessary to be -30 mgKOH / g, preferably 15-25 mgKOH / g. If the acid value of the polyester resin is less than 10 mgKOH / g, the amount of the epoxy resin-based curing agent blended becomes too small, and even if a matting agent is added, a matte coating film cannot be obtained, which is not preferable. . On the other hand, when the acid value exceeds 30 mgKOH / g, the amount of the epoxy resin-based curing agent compounded becomes too large and the coating film yellows over time, which is not preferable.

The polyester resin of the present invention needs to have a hydroxyl value of 7 mgKOH / g or more, preferably 10 mgKOH / g or more. If the hydroxyl value of the polyester resin is less than 7 mgKOH / g, the crosslink density of the coating film becomes too low and sufficient mechanical strength cannot be obtained, which is not preferable.

A polyester resin satisfying the above conditions is prepared by esterification at a temperature of 200 to 260 ° C. by a conventional method using the above alcohol component and carboxylic acid component (including their ester forming derivative) as a raw material. Alternatively, after the transesterification reaction, under reduced pressure of 5 hPa or less, 2
It can be prepared by a method of carrying out a polycondensation reaction at a temperature of 00 to 300 ° C., preferably 230 to 290 ° C. to obtain a polyester having a high degree of polymerization, and further adding an acid component and an alcohol component to carry out a depolymerization reaction. Alternatively, after the esterification or transesterification reaction is carried out by a conventional method, under normal pressure or under reduced pressure of about 50 to 100 hPa, 200 to 3
It can also be prepared by a method of performing a polycondensation reaction at a temperature of 00 ° C, preferably 220 to 280 ° C until a predetermined intrinsic viscosity is obtained, and then adding an acid component to carry out an addition reaction. A known reaction catalyst or the like can be used in the esterification, transesterification reaction, and polycondensation reaction.

The resin composition for powder coating of the present invention comprises a polyester resin, an epoxy resin type curing agent having an epoxy equivalent of 250 g / eq or less, a curing agent having a functional group which reacts with a hydroxyl group of the polyester resin, and a matting agent. Should be included in a ratio satisfying the following formula and. 0.8 ≦ (A + B) /C≦1.2 ... 0.3 ≦ A / B ≦ 0.9, where A is the amount (equivalent amount) of carboxyl groups in the polyester resin, B is the amount of carboxyl groups in the matting agent (equivalent), and C is the amount of epoxy groups contained in the epoxy resin-based curing agent (equivalent).

If (A + B) / C in the formula is less than 0.8, the crosslink density of the coating film is lowered and the mechanical strength of the coating film is lowered, which is not preferable. On the other hand, if (A + B) / C exceeds 1.2, the compounding amount of the epoxy resin-based curing agent becomes too small and a matte coating film cannot be obtained, which is not preferable.

If A / B in the formula is less than 0.3, the blending amount of the polyester resin becomes too small, so that not only a matte coating film is not formed, but also the crosslink density becomes low and the coating film machine It is not preferable because the physical properties are deteriorated. In addition, the weight of the epoxy resin-based curing agent in the paint increases, and the coating film turns yellow over time, which is not preferable.
On the other hand, if A / B exceeds 0.9, the amount of the matting agent added is reduced, and a matte coating film cannot be obtained, which is not preferable.

The epoxy resin-based curing agent used in the resin composition for powder coating of the present invention has an epoxy equivalent of 250 g / eq.
Must be: If the epoxy equivalent of the epoxy resin-based curing agent exceeds 250 g / eq, the weight of the epoxy resin in the resin composition increases, and as a result, good weather resistance cannot be obtained, which is not preferable. As the epoxy resin type curing agent having an epoxy equivalent of 250 g / eq or less as described above, a liquid epi-bis type epoxy resin derived from bisphenol A and epichlorohydrin is preferable, and "Epototo YD-12" manufactured by Tohto Kasei Co., Ltd.
8 "," Epicoat 828 "manufactured by Shell Co.," DER 331 "manufactured by Dow Chemical Co., and the like.

If desired, a curing accelerator such as a phosphine compound may be added to the epoxy resin type curing agent. As the phosphine compound, triphenylphosphine is preferable, and "PP" manufactured by Ihara Chemical Industry Co., Ltd.
-360 ".

As the curing agent having a functional group that reacts with the hydroxyl group of the polyester resin used in the resin composition for powder coating of the present invention, an isocyanate curing agent is preferable. As the isocyanate-based curing agent, ε-caprolactam blocked isophorone diisocyanate blocked with a blocking agent such as ε-caprolactam, and uretdione-bonded isocyanate which is a self-blocking type are preferable. Examples of such ε-caprolactam blocked isophorone diisocyanate include “Vestagon B 1530” manufactured by Huls and “Clerane U-” manufactured by Bayer.
1 ", and examples of the uretdione-bonded isocyanate include" Vestagon BF 1 "manufactured by Huls.
540 ", but" Vestagon B 1530 "is preferable from the viewpoint of coating film performance. The amount of the curing agent having a functional group that reacts with the hydroxyl group of the polyester resin is 0.8 to 1.2 times the equivalent of the hydroxyl value of the polyester resin,
It is suitable to use 1.0 times equivalent.

If necessary, a curing accelerator such as a tin compound may be added to the curing agent having a functional group that reacts with the hydroxyl group of the polyester resin. As the tin-based curing accelerator, dioctyl tin maleate-based curing catalyst is preferable,
"Stann OMF" manufactured by Sankyo Machine Gosei Co., Ltd. may be mentioned.

The blending amount of each curing accelerator is 0.1 to 1.0 parts by mass with respect to 100 parts by mass in total of the polyester resin and the curing agent, and the smoothness of the coating film and the coating film. It is preferable in that the curability can be achieved at the same time.

The matting agent used in the resin composition for powder coating of the present invention is preferably an imidazoline salt compound of an aromatic polyvalent carboxylic acid, such as "Vestagon" produced by Huls.
B68 ”.

The powder coating composition of the present invention comprises a resin composition comprising the above polyester resin, a curing agent, a curing accelerator, and a matting agent, if necessary, a known leveling agent and other additives, for example, Titanium dioxide, precipitated barium sulfate,
It can be prepared by melt-kneading a mixture of pigments such as carbon black at 70 to 150 ° C. using a kneader or roll.

The powder coating composition of the present invention is excellent in weather resistance and is yellowed with time by coating the powder coating composition on an object to be coated and baking it at a temperature of 170 to 200 ° C. for 15 to 25 minutes. And gives a coating film having good smoothness and the like.

[0025]

The polyester resin for powder coating according to the present invention has good weather resistance without impairing various properties of the coating film by using a specific copolymerization component and a curing agent having good weather resistance. It seems that a matte coating film that does not yellow with time is obtained.

[0026]

EXAMPLES The present invention will be described in detail with reference to Examples and Comparative Examples. In addition, in the examples and comparative examples, the characteristic values of the polyester resin and the resin composition and the coating film performance were evaluated by the following methods. (1) Intrinsic viscosity An equal mass mixture of phenol and ethane tetrachloride was used as a solvent, and measurement was carried out at 20 ° C. (2) After acetylation with hydroxyl value acetic anhydride, 0.5 × 10 ³ mol /
It was determined by titration with a m ³ solution of potassium hydroxide in methanol. (3) Dioxane / distilled water = 10 with 0.5 g of acid value polyester resin
It was dissolved in 50 ml of a mixed solvent of 1/1 (mass ratio), heated under reflux, and titrated with a 0.1 × 10 ³ mol / m ³ solution of potassium hydroxide in methanol. (4) Ratio of copolymerization component Polyester resin is dissolved in deuterated trifluoroacetic acid, and ¹ H-NMR (JNM-LA400 manufactured by JEOL Ltd.)
Was measured and determined. (5) Smoothness The smoothness of the coating film was visually evaluated in the following two stages. Good: The coating film has few irregularities and has good smoothness. X: The coating film has large unevenness and has poor smoothness. (6) 60 degree specular gloss It was determined according to JIS K 5400, and a value of 30% or less was passed. (7) Mechanical strength (impact resistance test) In accordance with JIS K 5400, paint is applied so that the coating film contacts the spherical surface between the shooting die having a spherical surface with a diameter of 1.27 cm and the pedestal having a recess corresponding to it. A steel plate was sandwiched, and a weight of 1 kg was dropped vertically onto the steel plate to determine the height at which the coating film was destroyed. If this value was 30 cm or more, it was determined to be acceptable. (8) Accelerated weather resistance According to JIS K 5400, a sunshine weather meter (“WEL-SUN-HCH.B” manufactured by Suga Test Instruments Co., Ltd.
-BR type ") was used to determine the gloss retention rate after irradiation for 250 hours. If this value was 80% or more, it was determined to be acceptable. (9) Yellowing over time According to JIS K 5400, WEL-SUN-HCH
Irradiation was performed for 156 hours using a B / BR type sunshine weather meter (manufactured by Suga Test Instruments Co., Ltd.). The color tone of the coating film before and after irradiation was measured by a color difference meter (SEΣ80 manufactured by Nippon Denshoku Industries Co., Ltd.
Type) and ΔE was calculated according to the following formula. (ΔE) ² = (L ₀ −L) ² + (a ₀ −a) ² + (b ₀ −b)
² where L ₀ , a ₀ and b ₀ are the color tones (La
b), and L, a, and b are color tones (Lab) of the coating film after irradiation for 156 hours. Those with ΔE of 2.0 or less were accepted.

Example 1 90 mol parts of terephthalic acid, 10 mol parts of isophthalic acid, 100 mol parts of neopentyl glycol, and 20 mol parts of ethylene glycol were charged into an esterification reaction tank, and the pressure was 0.3.
The esterification reaction was carried out at MPaG and a temperature of 260 ° C. for 4 hours. After transferring the obtained esterified product to a polycondensation reaction tank, antimony trioxide was added at 4.0 × 10 ⁻⁴ mol / acid component 1
Molar amount was added, the pressure was reduced to 0.5 hPa, and polycondensation reaction was performed at 280 ° C. for 4 hours to obtain a polyester having an intrinsic viscosity of 0.45 dl / g or more. Next, to this polyester, 3 mol parts of neopentyl glycol and 1.5 mol parts of trimethylolpropane were added, and under normal pressure, at 270 ° C. for 1 hour, and then 5 mol parts of isophthalic acid were added to the polyester at 250 ° C. Depolymerization reaction was carried out for a period of time to obtain a polyester resin having the characteristic values shown in Table 1.

The obtained polyester resin, epi-bis type epoxy resin type curing agent ("Epototo YD" manufactured by Tohto Kasei Co., Ltd.
-128: Epoxy equivalent 190 g / eq "), triphenylphosphine-based curing accelerator (" PP-360 "manufactured by Ihara Chemical Industry Co., Ltd.), ε-caprolactam block type isophorone diisocyanate curing agent (" Bestagon B 1530 "manufactured by Huls). ), Dioctyl tin maleate-based curing catalyst (“Stan OM
F ”) and a matting agent (“ Vestagon B68 ”manufactured by Huls), and a butyl polyacrylate leveling agent (“ Acronal 4 manufactured by BASF ”).
F "), rutile type titanium dioxide pigment (" Taipec CR-90 "manufactured by Ishihara Sangyo Co., Ltd.), and precipitable barium sulfate (manufactured by Sakai Chemical Industry Co., Ltd.) are added in amounts (parts by mass) shown in Table 1,
Henschel mixer (Mitsui Miike Seisakusho "FM10B
Type)), and then melt-kneading at 120 ° C. using a co kneader (“PR-46 type” manufactured by Buss Co., Ltd.),
After cooling and pulverizing, the powder was classified by a wire mesh of 140 mesh (106 μm) to obtain a powder coating material. The obtained powder coating material was electrostatically coated on a zinc phosphate-treated steel sheet to a film thickness of 50 to 60 μm, and baked at 180 ° C. for 20 minutes. The results of evaluating the performance of the obtained coating film are shown in Table 1.

Examples 2 to 4 and Comparative Examples 1 to 8 The composition of the polyester resin, the resin composition, and the composition of the paint were changed as shown in Table 1, and a polyester resin was prepared in the same manner as in Example 1. A resin composition and powder coating were obtained.

[0030]

[Table 1]

The powder coatings obtained in the examples are powder coatings having a good matting state, not yellowing over time, and excellent weather resistance. The coatings have smoothness and mechanical strength. It was good. In Comparative Example 1, the intrinsic viscosity of the resin was low and the acid value was high, so the amount of the epoxy resin-based curing agent was large, the weather resistance of the coating film decreased, and the coating film turned yellow over time. In addition, since the curing speed was high, the smoothness of the coating film was poor. In Comparative Example 2, the intrinsic viscosity of the resin was high and the acid value was low, so the smoothness of the coating film was poor. Further, since the amount of the epoxy resin-based curing agent blended was too small, even if a matting agent was added, a matte coating film could not be obtained. Comparative Example 3 has a hydroxyl value of 7 m
Since it is less than gKOH / g and the crosslink density of the coating film is low,
Sufficient mechanical strength was not obtained. In Comparative Example 4, since the proportion of neopentyl glycol copolymerized was small, not only the weather resistance of the coating film was insufficient, but also the coating film yellowed over time. In Comparative Example 5, since (A + B) / C is less than 0.8, the cross-linking density of the coating film is low, sufficient mechanical strength is not obtained, and the epoxy resin curing agent is mixed in a large amount. However, the weather resistance of the coating film was insufficient and the coating film also yellowed over time.
On the other hand, in Comparative Example 6, since (A + B) / C exceeds 1.2, the compounding amount of the epoxy resin curing agent is small, and even if a matting agent is added, a matte coating film is not formed, Moreover, sufficient mechanical strength was not obtained. In Comparative Example 7, since A / B is less than 0.3, the blending amount of the polyester resin is small, a matte coating film is not formed, and the crosslink density is low, so that sufficient mechanical strength is obtained. I couldn't do it. Further, since the amount of the epoxy resin-based curing agent added was large, the coating film yellowed over time. In Comparative Example 8, since A / B was more than 0.9, the amount of the matting agent was small and a matte coating film was not obtained.

[0032]

EFFECT OF THE INVENTION According to the present invention, a polyester resin for powder coatings, which has good smoothness and mechanical strength, does not yellow with time and has a good weather resistance, A composition and a powder coating material using the same are provided.

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 4J029 AA01 AA03 AB01 AC01 AC02                       AD01 AD02 AD03 AE11 BA02                       BA03 BA04 BA05 BA08 BA10                       BD04A BD07A BF09 BF26                       CA02 CA04 CA06 CB05A                       CB06A CC05A CD03 CH02                       DB01 FC03 FC05 FC08 FC12                       KB02                 4J038 DB002 DD061 GA03 GA06                       KA03 KA08 MA14 NA01 NA04                       NA11 PA02

Claims (3)

[Claims] 1. An acid component is mainly an aromatic dicarboxylic acid, 80 mol% or more of an alcohol component is neopentyl glycol, and an intrinsic viscosity is 0.10 to 0.30 dl.
/ G, an acid value of 10 to 30 mgKOH / g, and a hydroxyl value of 7 mgKOH / g or more, a polyester resin for powder coatings. 2. The polyester resin according to claim 1, an epoxy resin-based curing agent having an epoxy equivalent of 250 g / eq or less, a curing agent having a functional group that reacts with a hydroxyl group of the polyester resin, and a matting agent, represented by the following formula and A polyester resin composition for powder coatings, which is contained in a ratio satisfying the above conditions. 0.8 ≦ (A + B) /C≦1.2 ... 0.3 ≦ A / B ≦ 0.9, where A is the amount (equivalent amount) of carboxyl groups in the polyester resin, B is the amount of carboxyl groups in the matting agent (equivalent), and C is the amount of epoxy groups contained in the epoxy resin-based curing agent (equivalent). 3. A powder coating material using the polyester resin composition for powder coating material according to claim 2.